Method and apparatus for detecting quenching of a coil for a superconducting magnet

Abstract

Quenching of a coil for a superconducting magnet is detected by placing a temperature sensor proximate the coil of the superconducting magnet and monitoring the temperature sensor for a rise in temperature of the coil of the superconducting magnet. AC and DC field variations of the coil of the superconducting magnet do not substantially adversely affect such temperature monitoring, thus facilitating reliable and accurate detection of such quenching. This accurate and reliable detection of quenching assures that the superconducting magnet can be shut down in a controlled manner, so as to prevent damage thereto when quenching occurs. The method and apparatus of the present invention finds particular use in maglev applications.

What is claimed is: 
     
       1. An apparatus for detecting the quenching of a coil for a superconducting magnet, the apparatus comprising: a variable resistive temperature sensor disposed proximate the coil of the superconducting magnet and operable to generate an output voltage which is proportional to the temperature of the coil when a current is supplied to the temperature sensor; and   a quench detection circuit in direct electrical communication with the temperature sensor and comprising: a substantially constant current source electrically connected to the temperature sensor for supplying current thereto; and   a monitoring circuit electrically connected to the temperature sensor for reading the output voltage of the temperature sensor;     wherein AC and DC field variations of the coil of the superconducting magnet do not substantially adversely affect the reading of the output voltage by the monitoring circuit, thus facilitating reliable and accurate detection of the quench.   
     
     
       2. The apparatus of claim 1 wherein the temperature sensor comprises a carbon glass resistor which produces a voltage drop in the quench detection circuit corresponding to the temperature of the coil of the superconducting magnet. 
     
     
       3. The apparatus of claim 2 wherein the monitoring circuit is operable to compare the voltage drop across the carbon glass resistor to a reference voltage source representative of a desired operating temperature of the coil of the superconducting magnet. 
     
     
       4. The apparatus of claim 3 further comprising: a power supply electrically connected to the coil for supplying current thereto;   a latching relay electrically connected to the monitoring circuit and responsive to a difference in the voltage drop across the carbon glass resistor and the reference voltage source such that the latching relay is triggered when the difference exceeds a predetermined limit; and   a circuit breaker electrically connected to the coil, the latching relay, and the power supply;   the circuit breaker being openable by the latching relay to reduce current flow from the power supply through the coil when the difference between the voltage drop and the reference voltage exceeds the predetermined limit.   
     
     
       5. The apparatus of claim 3 wherein the monitoring circuit comprises a differential amplifier electrically connected to the temperature sensor and the reference voltage source. 
     
     
       6. The apparatus of claim 5 wherein the monitoring circuit further comprises an amplifier electrically connected to the differential amplifier and the temperature sensor for amplifying the voltage drop across the carbon glass resistor prior to electrically communicating the voltage drop to the differential amplifier. 
     
     
       7. A method for detecting the quenching of a coil of a superconducting magnet, the method comprising the steps of: (a) disposing a variable resistive temperature sensor proximate the coil;   (b) supplying a substantially constant current to the temperature sensor so as to cause the temperature sensor to generate an output voltage which is proportional to the temperature of the coil; and   (c) monitoring the temperature of the coil by reading the output voltage of the temperature sensor via a quench detection circuit which is in direct electrical communication with the temperature sensor.   
     
     
       8. The method of claim 7 further comprising the step of: (d) reducing the flow of current to the coil when the temperature thereof exceeds a desired operating temperature.   
     
     
       9. The method of claim 8 wherein step (b) comprises supplying current to the temperature sensor from a current source of the quench detection circuit. 
     
     
       10. The method of claim 8 wherein: step (b) comprises producing a voltage drop across the temperature sensor which is generated therefrom as the output voltage; and   step (c) comprises comparing the output voltage to a reference voltage representative of the desired operating temperature of the coil.   
     
     
       11. The method of claim 10 wherein the quench detection circuit includes a differential amplifier for comparing the output voltage to the reference voltage, and step (c) comprises amplifying the output voltage from the temperature sensor prior to the transmission thereof to the differential amplifier. 
     
     
       12. The method of claim 10 wherein step (d) comprises: (1) triggering a latching relay which is electrically connected to the quench detection circuit and responsive to a difference between the output voltage and the reference voltage when the difference exceeds a predetermined limit; and   (2) opening a circuit breaker which is electrically connected to the latching relay and operative to reduce the flow of current through the coil when opened.